[aaroncheungzy]

Summary

This PR improves four areas of the connection experience: connection animation and feedback, automatic connection on audio playback, battery detection, and the tray Quit button. Supersedes #253.

1. Connection animation and feedback

• Replace Windows system notifications with an application-owned card styled consistently with the battery window, with light/dark theme support.
• Show an animated indeterminate progress indicator while connecting, and reuse the same card for progress and errors.
• On a successful connection, dismiss the connection card and show battery information without an extra "Connected" notification.
• Make a single tray click connect when disconnected or show battery information when already connected; remove the dedicated double-click action.
• Update the setting description and all existing translation catalogs.

2. Automatic connection on audio playback

• Add Connect automatically when audio starts playing, off by default and independent of the tray-click setting. Both options use the same selected paired Bluetooth audio device.
• When playback starts, connect only if the selected device is disconnected. Already-connected automatic checks stay silent, and in-flight requests are reused.
• After a failure, require at least 30 seconds and a new playback start before retrying; do not repeatedly reconnect during continuous playback.
• Check Windows output audio sessions on a background worker every 250 ms, excluding this application's own audio. Disable monitoring when the setting is off.
• Running streams count as playback through quiet passages and muted output. A 1.5-second inactive interval recognizes a stop; apps that keep streams running while paused may delay a subsequent start.

The new configuration key is audio_auto_connect_enabled, with a default value of false.

3. Battery detection and source filtering

• Prevent battery readings from repeatedly jumping between inconsistent values when conflicting advertisement sources are merged.
• Check overlapping battery reports for consistency, allowing adjacent 10% buckets. An initial partial conflicting report can be replaced by a more complete report with a signal at least 10 dB stronger.
• Preserve existing latest-available merging, expiry behavior, and genuine battery changes. Broadcast readings retain their existing 10% granularity.
• Add a regression fixture containing 48 anonymized observations, without Bluetooth addresses or encrypted payloads.

Source selection remains a heuristic; unauthenticated broadcasts alone cannot prove that two advertisements belong to the same pair.

4. Tray Quit button

• Fix Quit being canceled by the battery window's close-to-tray handler.
• Queue an explicit QCoreApplication::exit(0) on the GUI thread, preserving normal application destruction and worker cleanup.
• Keep normal battery-window closing/hiding behavior.
• Add a child-process regression test that triggers the real tray Quit action with the battery window visible and verifies that the process exits.

No new dependencies are introduced.

Validation

• Manually tested on Windows 11 25H2 with AirPods 4 with Active Noise Cancellation and the bilibili web player, including playback-triggered connection and the subsequent battery-display and tray-exit fixes.
• Local x64 RelWithDebInfo build passed with Qt 6.8.3 and MSVC 19.51 (Visual Studio 2026 Build Tools).
• ctest --test-dir Build -C RelWithDebInfo --output-on-failure: 12/12 test targets passed. The optional native tone smoke test is opt-in and skipped in the standard run.
• Tests cover independent settings, persistence, playback edges, cooldown, duplicate requests, already-connected behavior, monitor shutdown, concurrent manual clicks, battery-source conflicts in both arrival orders, captured packet replay, and process exit with a visible battery window.
• UI tests use in-memory settings; production settings were unchanged during the final test run.
• C++ formatting and git diff --check passed.

Screenshots

Captured by the local UI tests:

Light notification	Dark notification